Magnetically journalled electrical drive

ABSTRACT

A magnetically journalled electrical drive comprises a magnetically journalled electrical machine with machine and magnetic bearing windings which are inserted in the stator or rotor for the production of the torque and the suspension force and an analog or digital electronic circuitry for control, regulation, monitoring and excitation of the magnetically journalled machine. The magnetically journalled machine is equipped in the stator or rotor with separate single or multiple looped windings for the production of torque ( 30, 31, 32, 33 ) and for the production of suspension force ( 34, 35, 36, 37 ), with at least one of the windings being formed as a concentrated winding with pronounced winding poles.

[0001] The invention relates to a magnetically journalled electricaldrive in accordance with the preamble of the independent claim.

[0002] Magnetic journalling technology opens up fields of application ofmachine and apparatus construction with extremely high requirements onthe speed of rotation region, the lifetime, the purity and the sealingtightness of the drive system—thus substantially fields of applicationwhich can not or can only with difficulty be realised using conventionaljournalling techniques. Various embodiments, such as for example highspeed milling and grinding spindles, turbocompressors, vacuum pumps, orpumps for chemical or medical products of high purity are already beingequipped with magnetic bearings.

[0003] A conventional magnetically journalled electrical machine(FIG. 1) requires, in addition to a machine unit 1, two radial magneticbearings 2 and 3 respectively, an axial magnetic bearing 4, twomechanical interception bearings 5 and 6 respectively and a total ofthirteen power controllers 7, 8, 9 and 10 for the excitation of themotoric and magnetic bearing loops.

[0004] There are proposals (FIG. 2) in the literature for integratingmachines and radial magnetic bearings in a magnetic stator unit. Twoseparate winding systems 11 and 12 for the torque and suspension forcewinding are inserted multiply layered into grooves in a stator. Bothwinding systems are three-looped and differ by one in the number of polepairs. The coils are distributed over a plurality of grooves. Theexample of FIG. 2 shows:

[0005] a four-pole machine winding 11 (outside): first loop 13, secondloop 14, third loop 15

[0006] a two-pole suspension winding 12 (inside): first loop 16, secondloop 17, third loop 18.

[0007] The arrows (without reference symbols) from the rotor in thedirection towards the stator or from the stator in the direction towardsthe rotor stand for the direction of the magnetisation of the fourmagnetic rotor segments (e.g. radial or diametral magnetisation).

[0008] In applications which require no rigid-axis rotor guidance, suchas for example in ventilators, fans, pumps or mixers, the axial magneticbearing and the second radial magnetic bearing can be omitted from theintegrated machine-magnetic-bearing embodiment. A prerequisite for thisis a disc-shaped embodiment of the rotor with a length dimension (FIG.3) which is small with respect to the rotor diameter. Thus a passivestabilisation of the rotor position in the axial direction and the tiltdirections can be achieved via the magnetic traction 41 between thestator 39 and the rotor 40.

[0009] In many cases however the complicated and expensive systemconstruction and therewith the higher manufacturing costs stand in theway of the technical use of magnetic journalling. The object of theinvention consists therefore in the simplification of the mechanicalconstruction of the machine and magnetic bearing unit taking intoconsideration the electronic excitation which is suitable for this.

[0010] This satisfaction of this object in accordance with the inventionresults from the features of the independent claims. Preferredembodiment variants are characterised by the features of the subordinateclaims. Of particular advantage in the satisfaction of the object inaccordance with the invention is the considerably simplified stator orrotor construction respectively and the winding construction of themagnetically journalled machine with respect to previously knownsolutions as well as the saving of power controllers. Thus for exampleonly three loops and six coils are required for a magneticallyjournalled single phase motor.

[0011] Exemplary embodiments of the invention are explained in thefollowing with reference to the drawings. Shown in schematicillustration are:

[0012]FIG. 1 an exemplary embodiment of a conventional magneticallyjournalled electrical machine,

[0013]FIG. 2 an exemplary embodiment of a conventional magneticallyjournalled electrical machine in which the machine and the radialmagnetic bearing are integrated into a magnetic stator unit,

[0014]FIG. 3 a possibility of passive stabilisation of the rotor in theaxial direction as well as in the tilt directions,

[0015]FIG. 4 an exemplary embodiment of a stator of the magneticallyjournalled electrical drive in accordance with the invention,

[0016]FIG. 5 An exemplary embodiment of the electrical drive inaccordance with the invention with a technical winding variant for anouter rotor.

[0017]FIG. 6 an exemplary embodiment of an electrical drive with aplurality of distributed coils,

[0018]FIG. 7 an exemplary embodiment of a possible bridge circuit forthe excitation of the electrical drive,

[0019]FIG. 8 an exemplary embodiment of the magnetically journalleddrive in accordance with the invention with sinewed concentric windingsand with pronounced poles and auxiliary poles,

[0020]FIG. 9 an illustration of the angle-dependent force fluctuationsin non-sinusoidal stator current layer distributions and non-sinusoidalexcitation field distribution in the air gap,

[0021]FIG. 10 an exemplary embodiment of the drive in accordance withthe invention with an asymmetric sheet metal cut in the region of thewinding poles,

[0022]FIG. 11 an exemplary embodiment of a drive in accordance with theinvention with an auxiliary magnet for ensuring the start-up in a motoroperation with an alternating field,

[0023]FIG. 12 a possibility of the controlled rolling down of the rotorat the stator poles,

[0024]FIG. 13 an exemplary embodiment of a drive in accordance with theinvention with short circuit rings which are attached one-sidedly at thestator poles,

[0025]FIG. 14 an exemplary embodiment of a drive in accordance with theinvention with a special shaping of the magnet segments for achieving asinusoidal excitation field distribution in the air gap and

[0026]FIG. 15 an exemplary embodiment of a stator of the magneticallyjournalled drive in accordance with the invention with the possibilityof a rotary field production both in the machine and in the radialbearing.

[0027] The machines can be operated as a motor or as a generatordepending on the application. FIG. 4 shows an embodiment of amachine-magnetic-bearing unit (the stator is e.g. fitted in an aluminiumring or aluminium cylinder respectively for a better cooling) withconcentrated diameter windings and pronounced poles. Concentratedwindings are to be understood here to mean windings of which the coilsare not distributed over a pole division and at the same time(magnetically effectively) displaced with respect to one another. Thusthe coils 34 and 35 respectively are considered to be concentrated. Bypronounced poles are meant ferromagnetic poles or air coil poles whichare surrounded by a concentrated winding. In this category are includedfor example limb poles 99, which are surrounded by the concentratedwinding, or singly or multiply divided poles such as 99 and 100, whichare magnetically enclosed by the concentrated coil 36. The windings canalso be fractionally pitched, i.e. executed with a winding width smalleror larger than a pole division. An exemplary embodiment for this isillustrated in FIG. 8. In a strong fractional pitching it is undercertain conditions favourable to close the pole gap which arises throughthe shortening of the pole width with a ferromagnetic auxiliary pole 86.The functions of the production of torque and suspension force arerealised in the arrangements in FIG. 4 and FIG. 8 by two windingsystems: A single-loop, four-pole machine winding and a two-loopmagnetic bearing winding.

[0028] The machine loop is formed of the coils 30, 31, 32 and 33, thefirst magnetic bearing loop is formed of the coils 34 and 35 and thesecond magnetic bearing loop of the coils 36 and 37. The concentratedcoils of the machine loop form pronounced poles (here: limb poles) withthe ferromagnetic material. Depending on the requirements they can beconnected to one another in series or in parallel and upon excitationwith an alternating current develop a four-pole rotary field whichsuffices in order for example to produce a torque at a four-polepermanent magnet rotor. The first and the second magnetic bearing loopare arranged at an angle of ninety degrees to one another. A two-polerotary field is built up via a corresponding current excitation of themagnetic bearing loops for the setting of the radial suspension force inamplitude and phase. The coils of a machine or magnetic bearing loop inFIG. 4 are connected in series or in parallel. The magnetic bearingcoils 34 and 35 and/or the coils 36 and 37 can when required in eachcase be combined to a single coil and form concentrated windings.

[0029]FIG. 5 illustrates a technical winding variant for an outer rotordrive with likewise a single-loop, four-pole machine winding 67, 68, 69,70 and a two-loop, two-pole magnetic bearing winding with the first loop71, 72 and the second loop 73, 74, which is arranged perpendicular tothe latter. The two loops of the magnetic bearing winding can also berotated by 45° and laid in grooves of the machine winding so that aconstruction similar to that in FIG. 4 results. Furthermore, the coils71, 72 and 73, 74 can in each case be combined to form one coil. Asconcerns the machine loop, two mutually oppositely lying coils, e.g. 68,70, could be dispensed with. The outer rotor of the arrangement in FIG.5 is preferably executed as a four-pole ring or as a bell.

[0030] Alternatively to the arrangement in FIG. 4 and FIG. 5 the machinewinding or the magnetic bearing winding can also be built up of aplurality of (illustrated as two) distributed coils 75, 76 (FIG. 6).Accordingly, one recognises in FIG. 6 a first loop connection 77 and asecond loop connection 78 or, respectively, the further connection tothe next adjacent winding pole with the opposite winding sense.

[0031] The determination of the individual loop currents is done bytaking into account the specified desired values and the actual valuesfor example of the rotor position and speed of rotation, the rotor angleof rotation or torque after the evaluation of the sensor signals for therotor position and rotor angle of rotation by means of an analog circuitor of a high speed computer unit. The signals which are determined areamplified by a power electronic circuitry and supplied to the threeloops via clocked switches or analog power amplifiers. A possible bridgecircuit is given in FIG. 7. The machine loop is designated by 24, thetwo magnetic bearing loops by 25 and 26. Instead of the impression of acurrent an impression of the voltage can also take place taking intoaccount the characteristic of the regulation path.

[0032] The rotor type of the machine can be chosen freely, in particularwhen the machine operation takes place via a rotary field instead of analternating field. Usable are for example permanent magnet rotors,short-circuit cage rotors, rotors with an electrically highly conductingmetal jacketing instead of the short-circuit cage or reluctance rotorswith angle-dependent air gap variations.

[0033] In the event of insufficient fractional pitch or distributionrespectively of the windings and in the event of non-sinusoidalexcitation field distributions, angle dependent radial forcefluctuations 42, such as are illustrated for example in FIG. 9, arisethrough the harmonic content of the air gap fields in the currentexcitation of a loop of the radial bearing winding in accordance withFIG. 4, FIG. 5 or FIG. 8 with a constant current amplitude when therotor is rotated. This effect should be taken into account in thecurrent excitation of the windings in order to achieve a good operatingbehaviour.

[0034] A sufficiently sinusoidal excitation field distribution can beachieved in the use of permanent magnet rotors 85 for example through ashaping 82 with an angularly dependent air gap between the rotor and thestator 84 in accordance with FIG. 14. A diametral magnetisation of thepermanent magnets also acts favourably with respect to a sinusoidalfield distribution. The ferromagnetic rear contact or yoke of the rotoris designated by 83. For reasons of cost it can however be advantageousto use concentrated windings and radially or diametrally magnetisedmagnets without a special shaping.

[0035] Since only an alternating field is available for the machineoperation in the magnetically journalled machine in FIG. 4 or FIG. 5respectively, an auxiliary torque is to be provided where appropriate atthe time point of the start-up for overcoming the dead zone. This canfor example be done through an asymmetrical sheet metal cut 38 in theregion of the winding poles (FIG. 10). A further proposed solution (FIG.11) provides one or more auxiliary magnets 43 which are arranged axiallyor radially with respect to the rotor, and which for example bring thefour-pole permanent magnet rotor 50 into a favourable starting position44 with the angle ψ as a result of their drawing force. In the position45 of the magnet pole boundary the starting torque would be zero with anarbitrarily high current. The winding poles are indicated by 46, 47, 48and 49. In order to assist the drawing force the auxiliary magnets canadditionally be provided with an iron yoke.

[0036] A change in the magnet pole position could also be producedthrough a rolling down (FIG. 12) of the rotor 66 at the end side of theair gap of the stator pole 65 which is controlled by the magneticbearing part. As a result of the different diameters there results inthe rolling down a growing angular displacement between the magnet andstator poles so that the rotor can be rotated out of the dead zone inwhich a torque development is not possible. The midpoint movement of therotor during the rolling down is represented by 67. It may be necessaryto provide means at the periphery of the rotor and/or stator forpreventing a sliding between the rotor and the stator during the rollingdown movement (e.g. use of materials with high frictional values,roughening of the surfaces, toothing, etc.)

[0037] A further proposed solution is illustrated in FIG. 13. The statorpoles are provided on one side with a short-circuit ring 52 so that as aresult of the short-circuit currents a highly elliptical rotary fielddevelops in the air gap instead of the alternating field.

[0038]FIGS. 4, 5, 8 and 10 are to be considered as exemplary both withrespect to the number of pole pairs for the torque and suspension forceproduction and with respect to the loop number of the two windings.Modified numbers of pole pairs can also be realised, with it beingnecessary for the condition p_(M)=p_(ML)±1 to be fulfilled between thenumber of pole pairs P_(M) for the machine operation and the number ofpole pairs p_(ML) for the magnetic bearing operation. Throughenlargement of the loop number and the number of bridge branches in theelectronic power circuitry a rotary field machine can also be integratedin accordance with the invention into the magnetically journalled driveinstead of an alternating field machine.

[0039] A possible exemplary embodiment for this is illustrated in FIG.15. The stator contains two four-pole machine loops consisting of thecoils 87, 89, 91, 93 and 88, 90, 92, 94, which are connected in seriesor in parallel. The machine loops are displaced electrically withrespect to one another by 90° so that an armature rotary field for theproduction of a torque can be built up with a four-pole rotor withouttorque gap. This arrangement therefore requires no start-up help incontrast to preceding examples.

[0040] The diameter coils 95 and 97 form the two loops of the radialmagnetic bearing, which are displaced by 90°. Here a rotary fieldproduction is also possible. For the better utilisation of the availablewinding space two further coils 96 and 98 can be introduced and forexample the coil 96 can be connected to the coil 95 and the coil 98 canbe connected to the coil 97 to form a single loop in each case.

[0041] Another constructional variant, likewise with the numbers of polepairs two and one in the stator windings could also be realised with atwopole rotor. For this the single or multiple looped machine windingwould be chosen to be two-poled and the multiple looped magnetic bearingwinding to be four-poled. A further essential aspect of the invention,which is completely independent of the previously explained aspects, isbased finally on the recognition that it is possible to equip themagnetically journalled machine of the electrical drive in accordancewith the invention in the stator or rotor with separate windings for thetorque and suspension force production and in this to form the machinewinding in a single loop.

1. Magnetically journalled electrical drive comprising a magneticallyjournalled electrical machine with machine and magnetic bearing windingswhich are inserted in the stator or rotor for the production of thetorque and the suspension force and an analog or digital electroniccircuitry for control, regulation, monitoring and excitation of themagnetically journalled machine, characterised in that the magneticallyjournalled machine is equipped in the stator or rotor with separatesingle or multiple looped windings for the production of torque (30, 31,32, 33) and for the production of suspension force (34, 35, 36, 37),with at least one of the windings being formed as a concentrated windingwith pronounced winding poles.
 2. Electrical drive in accordance withclaim 1 characterised in that the magnetic bearing winding for theproduction of suspension force (34, 35, 36, 37) is formed in a number ofloops with the number of pole pairs PML for the development of a rotaryfield.
 3. Electrical drive in accordance with claim 1 characterised inthat the machine winding for the production of torque (30, 31, 32, 33)is formed in a number of loops with the number of pole pairsP_(M)=p_(ML)±1 for the production of a rotary field or with a singleloop for the production of an alternating field.
 4. Electrical drive inaccordance with claim 1 characterised in that the concentrated windingis formed as a diameter winding (30, 31, 32, 33).
 5. Electrical drive inaccordance with claim 1 characterised in that the concentrated windingis fractionally pitched and is thereby provided with a coil width whichis less than or greater than a pole division.
 6. Electrical drive inaccordance with one of the preceding claims characterised in that themagnetic bearing winding is formed in two loops (34, 35; 36, 37) and themotor winding is formed in one loop (30, 31, 32, 33); and in that thenumbers of pole pairs of the magnetic bearing winding (34, 35; 36, 37)and of the motor winding (30, 31, 32, 33) amount to one and two withoutevaluation of the sequence.
 7. Electrical drive in accordance with oneof the preceding claims characterised in that the rotor or the stator ofthe electrical drive is equipped with permanent magnets, with ashort-circuit cage, an electrically highly conducting metal jacketing ora reluctance cut.
 8. Electrical drive in accordance with one of thepreceding claims characterised in that in the case of a single loopedmachine winding a start-up aid for the reliable start-up is provided, inparticular in the form of an asymmetrical stator sheet metal cut (38),of one or more auxiliary magnets (43) or of one or more short-circuitrings (13); or in that a favourable start-up position of the rotor isset via a corresponding excitation of the magnetic bearing windingsthrough rolling down (67) of the rotor on the stator surface which facesthe rotor.
 9. Electrical drive in accordance with one of the precedingclaims characterised in that the magnetically effective part of therotor (40) and preferably also of the stator (39) is designed in disc,ring or bell shape with small axial dimensions relative to the radialdimensions so that a stable passive magnetic journalling of the rotor inthe axial direction and the two tilt directions which is sufficient forthe operation arises as a result of the force action (41) of themagnetic air gap fields.
 10. Electrical drive in accordance with one ofthe preceding claims characterised in that all windings, thus both themachine windings and the magnetic bearing windings, are formed asconcentrated windings.